Applications requiring Double Precision (DP) arithmetic executed on embedded CPUs without native DP support suffer from prohibitively low performance and power efficiency. Hybrid reconfigurable CPUs, allowing for reconfiguration of the instruction set at runtime, appear as a viable computing platform for applications requiring instructions not supported by existing fixed architectures. The authors' experiments on a Stretch S6 as prototypical platform show that limited reconfigurable resources on such architectures are sufficient for providing native support of DP arithmetic. Their design using a DP Fused Multiply-Accumulate (FMA) extension instruction achieves a peak performance of 200 MFlop/s and a sustained performance of 22.7 MFlop/s at a clock frequency of 100 MHz.